1. Field of the Invention
A check/relief valve intended for use in an inflatable packer system utilizes a positive displacement pump to inflate the packer elements. The positive displacement pump takes in abrasive drilling mud and pumps pressurized mud to one or more packer elements to inflate them and thereby seal off a zone in a well preparatory to testing.
Various problems may occur in such a system, among which are: a pressure loss in the system upstream of the packer elements; rupture of the packer elements due to overinflation; and pump damage due to overpressure.
2. Prior Art
An inflatable packer system in use today in the oil fields is described in U.S. Pat. No. 3,439,740 to G. E. Conover. The Conover system incorporates a positive displacement piston pump which takes in abrasive drilling mud and pumps pressurized mud to packer elements to inflate them. The pump has four pistons and associated inlets and outlets. There is a suction check valve in each inlet and a discharge check valve in each outlet of the pump.
The inlet check valves are constructed so that, when pump pressure exceeds the static pressure in the well bore by a predetermined amount, the suction check valves unseat so that each of the pistons will discharge fluid through a respective suction check valve rather than out through a respective discharge valve.
The discharge valves are constructed so that fluid may be pumped to the packer elements. In addition, there is a master check valve downstream from the discharge valves which is closed in the absence of pump pressure.
However, in a system such as Conover's, the suction/discharge valves have a short service life and require frequent maintenance due to the extreme service conditions involved in pumping abrasive fluid at extremely high pressures. In addition, if a valve fails, the pump section must be replaced due to the incorporation of the valves in the pump.